This invention relates generally to the field of metal working, and more particularly to an automated system of constructing frames of non-constant modulus.
The substructure of a metal building typically includes an array of main load resisting members, commonly called rigid frames. As the bending moment experienced by each such frame varies greatly over its length, tapered I-section beams are commonly used for rigid frames. Tapered beams avoid the material waste and added weight that would result from using beams of uniform modulus, designed to withstand the maximum bending moment experienced.
In the design of tapered beams, the required modulus is calculated from the design bending moment at each spot along the beam, and the cross-section of the beam at that point is designed to provide the required modulus.
A common way of varying the modulus of an I-beam is to vary the width of a uniformly thick web extending between the two flanges of the beam; the flanges may be of uniform width and thickness. U.S. Pat. No. 2,990,038 may be representative of such techniques, as it discloses a beam formed from non-orthogonal segments, the web thereof being formed of separate plates.
A tapered beam may be built up of a number of tapered webs, and associated flanges. The individual web sections are welded together to the proper column or rafter length, and then the flanges are welded on to create the I-section. Each tapered, generally trapezoidal web section is typically sheared or plasma cut from standard plate material, normally available in rectangular shapes four to five feet wide, and twelve to twenty feet long. Even with properly thought out layouts, a great deal of useless scrap can result. The amount of scrap generated can amount to as much as five percent of the weight of the rigid frame.
In sheet metal work, scrap reduction is a constant consideration, and much attention has been devoted to this problem over the years. Many patents addressing this problem have been awarded. For example, U.S. Pat. No. 1,813,761 describes a scrap-free method of cutting metal fence posts from material, and U.S. Pat. No. 2,990,038 suggests a method of forming structural beams with minimal waste.